1. Field of the Invention
The present invention relates to an image forming apparatus which forms a multicolor image by transferring, onto a material on which images are to be transferred (hereinafter called a “transfer-target material”), images sequentially formed on image carriers through use of a developing agent by means of a plurality of development units.
2. Description of the Related Art
In a hitherto-known image forming apparatus, images are sequentially formed, by use of a developing agent, on surfaces of a plurality of image carriers (a single image carrier in the case of a so-called four-cycle system), on each of which an electrostatic latent image is formed, by use of a plurality of development units. These images formed by use of the developing agent (such images will be called “developing-agent images” throughout the specification) are sequentially transferred onto a transfer-target material, such as paper or an intermediate transfer element, in a superimposed manner to thus form a multicolor image (see JP-A-2002-31933).
In such an image forming apparatus, when the developing-agent image formed on the image carrier is transferred to a transfer-target material, a portion of the developing agent forming the developing-agent image is not transferred and remains on the image carrier. The developing agent (a waste developing agent) adhering to the image carrier after transfer of such a developing-agent image becomes a “post-transfer residual ghost” which is transferred to a location other than that of an originally-intended image, thereby adversely affecting formation of an image after one rotation of the image carrier. In order to prevent exertion of adverse effect on formation of an image, which would otherwise be caused by such a waste developing agent, a known image forming apparatus is provided with a cleaner which is placed so as to oppose the image carrier and scrapes off the waste developing agent.
As an image forming apparatus for which an attempt has been made to achieve miniaturization and cost cutting without use of the cleaner, there is known an image forming apparatus which adopts a synchronous development-and-cleaning system, wherein an electrostatic latent image on the surface of an image carrier is developed by use of a development unit, and a waste developing agent adhering to an area other than the electrostatic latent image from the image carrier is recovered (see Japanese Patent No. 3154757).
This synchronous development-and-cleaning system corresponds to a method for recovering the waste developing agent adhering to the location other than the electrostatic latent image with use of the development unit through adsorption and by utilization of the fact that an area on the surface of the image carrier, except the location where the electrostatic latent image is formed, becomes higher in electric potential than the development unit.